This invention relates to the high temperature vapor coating of an article, and more particularly, to a container used for such coating.
Certain articles operating at elevated temperatures in an oxidizing atmosphere have been provided with environmental protection in the form of coatings of various types. For example, components such as gas turbine engine turbine blades and vanes operating at high temperatures typically experienced in the turbine section of the engine frequently include metallic surface coatings alone or in various combinations with other materials. Such coatings are capable of resisting the oxidation, corrosion and sulfidation conditions generated during high temperature operation.
Application methods for such coatings include depositing a vapor of one or more protective materials, for example aluminum or alloys including aluminum to provide a form of aluminide coating, on an article surface at high temperatures. Such a method is conducted in a nonoxidizing atmosphere within a coating container or chamber, sometimes called a part of the coating tooling. The coating vapor can be generated within the container in which the article is held or can be generated outside of such container and then introduced into the container to react with a surface of an article to be coated. Generally the container, connected with means to provide the nonoxidizing atmosphere, is placed for coating within a heating means such as a furnace. This type of coating and its associated coating tooling has been described widely in the coating art, particularly as it relates to coating of gas turbine engine components.
It has been a practice in the high temperature vapor coating art to use coating containers made of metal, at least in part because of their good thermal conductivity. However, it has been observed in connection with the use of such metal containers for coating at high temperatures, for example in the range of about 1700-2200.degree. F., that walls of the containers react with the coating vapor, becoming coated themselves along with the article or articles within the container. More importantly, as they become coated the containers frequently distort and crack. As a result, they no longer can be sealed during coating, resulting in loss of coating vapor and failed coating on the article. Consequently, the metal containers must be discarded and replaced periodically, and monitored prior to each use to assure good coating.